Currently, there is a great development in display devices capable of providing stereoscopic display. Such stereoscopic display devices are roughly classified into a type that requires the use of eyeglasses and a type used with naked eyes. Especially, the type capable of being used with naked eyes requires no trouble of wearing eyeglasses and is expected to be used broadly in the future.
As the stereoscopic display device employing a system that makes it possible to achieve stereoscopic display with naked eyes, there are the types having a light-ray distribution unit such as a lenticular lens or a parallax barrier placed on a front face or a back face of a display panel.
In a case of two-eye type of such system, employed is a structure with which right-eye pixels and left-eye pixels are prepared within the display panel, respectively, so that a video displayed on the eight-eye pixels reaches the right eye of a viewer via the lenticular lens or the parallax barrier while a video displayed on the left-eye pixels reaches the left eye.
In a case of a multi-eye type (n-viewpoints) that is expansion of the above-described two-eye type, pixels for the n-viewpoints are prepared in the display panel, and videos for two viewpoints among the n-viewpoints reach the left and right eyes of the viewer, respectively,
The light-ray distribution unit such as the lenticular lens or the parallax barrier of those naked-eye type stereopsis systems is often bonded while the mutual positioning relation thereof with respect to the display panel is fixed. Thus, the region (hereinafter, referred to as a stereopsis region) where the images to be displayed are perceived as stereoscopic by the viewer is fixed to be in a specific range.
In a case where the viewer shifts the position under such circumstance, the viewing position thereof changes as well. Thus, the positions of the eyes of the viewer may become out of the stereopsis region and flat views are to be viewed or there may be generated a phenomenon of inverted visions where a left-eye image makes incident on the right eye and a right-eye image makes incident on the left eye. Under a state of such inverted vision, the viewer cannot acquire proper stereopsis, e.g., the viewer perceives originally popup videos to be drawn back, which causes the viewer to feel a sense of discomfort and fatigue.
Therefore, there is developed a viewpoint following system employing a technique which detects the position of the head part of the viewer and displays a stereoscopic reproduced image in accordance with that position. For example, technical content as shown in following Patent Documents 1 to 3 are known.
Patent Document 1 discloses the content of a technique which detects positions of each of both eyes of a viewer, switches display pixels for displaying a right-eye image and a left-eye image in accordance with signals generated based on the detection result, and expands a stereopsis region thereby.
Patent Document 2 discloses a light directivity control method which detects viewpoints of a viewer and physically drives a lenticular lens in accordance with the detection result so as to enable display videos to follow the viewpoints of the viewer.
Meanwhile, the three-dimensional display device disclosed in Patent Document 3 employs a system with which a liquid crystal lenticular lens constituted with a liquid crystal lens is disposed on the whole plane of a display panel and a refractive index distribution of the liquid crystal lenticular lens is changed in accordance with the position of a viewer so as to reproduce a stereoscopic image at a significant position for the viewer.
Now, the structural content of the three-dimensional display device of Patent Document 3 will be described in a more specific manner by referring to FIG. 23 and FIG. 24.
As shown in FIG. 23, this three-dimensional display device 100 includes a liquid crystal panel 101, an optical characteristic variable lens 102, a head-part detection unit 103, and an optical characteristic variable lens control unit 104. When the head part of the viewer moves, this structure achieves processing in which the head-part detection unit 103 upon detecting the move transmits positional information of the head part to the optical characteristic variable lens control unit 104, and the optical characteristic variable lens control unit 104 changes the drive so as to change the characteristic of the optical characteristic variable lens 102 based on the positional information.
As shown in FIG. 24 that is a cross-section view illustrating the details of the structure of the optical characteristic variable lens 102, the optical characteristic variable lens 102 includes: a liquid crystal 105; a glass substrate 108 on which an electrode array 106 with strip-type electrodes 106a, 106b, 106c, - - - , 106h arranged thereon is formed; and a glass substrate 109 with an electrode 107 formed on the plane thereof. Further, as shown in FIG. 24, the electrode array 106 and the electrode 107 are disposed to oppose to each other, and the liquid crystal 105 is filled between the gap formed therebetween.
By employing such structure, it becomes possible to electrically control the optical characteristic of the lens since the distribution shape of the refractive index of the aggregate of liquid crystal molecules, the entire level of the refractive index, and the pitch of the refractive index distribution repeated periodically can be controlled through changing the pattern of the voltage to be applied to the electrode array 106.
Patent Document 1: Japanese Patent No. 2662252
Patent Document 2: Japanese Unexamined Patent Publication Hei 2-44995
Patent Document 3: Japanese Patent No. 2920051
However, with the system where the right-eye image and the left-eye image are switched in accordance with the detection result of the positions of the both eyes of the viewer like the technique of Patent Document 1, there are such inconveniences that the observed views may become discontinuous or that stereopsis cannot be achieved at the location where the positions of the eyes of a viewer is switched.
Further, with the system disclosed in Patent Document 2 where the lenticular lens is physically driven, the relative positions of the display panel and the lenticular lens are required to be controlled extremely accurately. Thus, it is required to use a precision mechanical system, which generates issues of increasing the size of the device and the weight thereof. Furthermore, it is required in this case to move a relatively large lenticular lens, so that the responsiveness of position control in the display space becomes poor. In addition, since employed is the structure where the lenticular lens is moved only within a plane that is in parallel to the display panel, the range following the head part becomes also limited to the plane that is in parallel to the display.
Further, with the system employed in the three-dimensional display device of Patent Document 3, the number of wirings for corresponding to the electrodes 106a, 106b, 106c, - - - , 106h is required in order to set the voltage individually for each of the electrodes 106a, 106b, 106c, - - - , 106h. Therefore, it is required to connect a great number of signal supply wirings, so that manufacture of the optical characteristic variable lens becomes complicated. Further, with the technique employed herein, the minimum unit when making adjustment according to the move of the viewer depends on the wiring pitch, so that the adjustment becomes discontinuous.
The present invention is designed in view of the foregoing issues. Especially, it is the object of the present invention to provide a light-weight lenticular lens element for displaying proper stereoscopic images smoothly according to the position fluctuation of the viewer with a simple structure, a stereoscopic display device having the liquid crystal lenticular lens element, a terminal device having the stereoscopic display device loaded thereon, and a driving method thereof.